1. Field of the Invention
The present invention relates to sound measuring apparatuses and methods and to audio signal processing apparatuses. More specifically, the present invention relates to a sound measuring apparatus and method for measuring a sound-arrival delay time from a speaker to a microphone on the basis of a result obtained by outputting a test signal from the speaker and picking up the test signal using the microphone. The present invention further relates to an audio signal processing apparatus having a function for measuring the sound-arrival delay time.
2. Description of the Related Art
In audio systems of the related art, in particular, an audio system in which audio signals are output from multiple channels, a test signal such as a sine-wave or time stretched pulse (TSP) signal is output from a speaker, and is picked up by a microphone located at a different place from the speaker. The result is used to measure a delay time (sound-arrival delay time) until the sound output from the speaker arrives at the microphone.
FIG. 12 shows an example technique of the related art.
In FIG. 12, a TSP signal is used as the test signal. As well known in the art, the TSP signal is generated by shifting the phase of an impulse signal shown in FIG. 12. Thus, the TSP signal output from the speaker and picked up by the microphone is subjected to a fast Fourier transform (FFT) and phase conversion so that the phase is shifted back by an amount of phase shift determined for generating the TSP signal, followed by an inverse fast Fourier transform (IFFT), to obtain an impulse response.
The thus obtained impulse response includes information on the delay time until the sound output from the speaker arrives at the microphone. Specifically, if the distance between the speaker and the microphone is not zero, a rising position of the impulse response obtained from the picked up TSP signal is delayed behind a rising position of an impulse signal that the TSP signal to be output from the speaker is based on, and the difference between the rising position of the impulse response and the rising position of the impulse signal is measured to determine the sound-arrival delay time (namely, a delay time DT shown in FIG. 12).
In view of the foregoing description, referring to FIG. 12, first, a TSP signal is output from a speaker for a predetermined period of time, as indicated by an output signal shown in FIG. 12, so that the TSP signal is repeatedly output for a plurality of cycles.
A microphone starts to pick up the TSP signal, as indicated by a picked up audio signal shown in FIG. 12, after the lapse of a predetermined time from the start of the output of the TSP signal. The microphone also picks up the TSP signal for the predetermined period of time so that the TSP signal of the plurality of cycles can be picked up.
The start of the pickup operation is synchronized with the beginning of one cycle of the TSP signal obtained as the output signal in the manner shown in FIG. 12. As shown in FIG. 12, since the speaker starts to output the TSP signal from the beginning of one cycle, the pickup operation is started in synchronization with the beginning of one cycle of the TSP signal, thus allowing a phase shift between the output TSP signal and the picked up TSP signal to be easily obtained by measuring the rising position of the impulse response calculated from the picked up audio signal starting from the beginning (0th clock) of one cycle.
In the technique shown in FIG. 12, the phase shift between the output TSP signal and the picked up TSP signal is measured as the deviation of the rising position of the impulse response described above.
Specifically, first, the picked up TSP signal of the plurality of cycles is added and averaged in the manner shown in FIG. 12. The adding and averaging operation relatively reduces the level of noise that is not synchronized with the cycles, such as background noise, and increases the signal-to-noise (S/N) ratio of the measured response signal. The result of the adding and averaging operation is subjected to FFT, phase conversion, and IFFT, as described above, to obtain an impulse response, and the deviation between the rising position of the obtained impulse response and the rising position of the original impulse signal that has not been output is measured to measure the sound-arrival delay time, namely, the delay time DT shown in FIG. 12.
Since the pickup operation starts in synchronization with the beginning of the output TSP signal, the measurement of the delay time DT based on the obtained impulse response is actually performed by determining which clock the impulse response rises at.
Techniques of the related art are disclosed in Japanese Unexamined Patent Application Publications No. 2000-097763 and No. 04-295727.